Method and apparatus for estimating remaining capacity of secondary battery

ABSTRACT

There is provided a battery pack system with estimation accuracy of a remaining capacity of a secondary batter enhanced. A current accumulation coefficient correction section  109  calculates a correction amount α with respect to a current accumulation coefficient k in accordance with a battery electromotive force Veq from an electromotive force calculation section  105 . A remaining capacity calculation section  112  estimates a remaining capacity SOC by current accumulation, based on the current accumulation coefficient k calculated from a correction amount α, and a charging efficiency η based on a currently estimated remaining capacity calculated by a charging efficiency calculation section  110.

TECHNICAL FIELD

The present invention relates to a method for estimating a remainingcapacity (SOC: State of Charge) of a secondary battery such as anickel-metal hydride (Ni—MH) battery to be mounted as a power source fora motor and a driving source for various loads, in motor-driven vehiclessuch as a pure electric vehicle (PEV), a hybrid electric vehicle (HEV),a hybrid vehicle with a fuel battery and a battery, or the like.

BACKGROUND ART

Conventionally, in an HEV, when an output from an engine is large withrespect to motive power required for driving, an electric generator isdriven with surplus motive power to charge a secondary battery. On theother hand, when an output from an engine is small, a motor is drivenwith the electric power from a secondary battery to output supplementarymotive power. In this case, a secondary battery is discharged. When asecondary battery is mounted on an HEV or the like, it is necessary tomaintain an appropriate operation state by controlling suchcharging/discharging, etc.

For this purpose, the voltage, current, temperature, and the like of asecondary battery are detected, and the remaining capacity (hereinafter,abbreviated as an “SOC”) of the secondary battery is estimated bycomputation, whereby an SOC is controlled so as to optimize the fuelconsumption efficiency of a vehicle. Furthermore, at this time, in orderto allow a power assist based on motor driving during acceleration to beoperated and to allow energy to be collected (regenerative braking)during deceleration with good balance, an SOC level is controlled asfollows. Generally, in order to set an SOC to be, for example, in arange of 50% to 70%, when the SOC decreases to, for example, 50%,control for excess charging is performed. On the other hand, when theSOC increases to, for example, 70%, control for excess discharging isperformed. Thus, it is attempted to approximate the SOC to the center ofcontrol.

In order to control the SOC exactly, it is necessary to exactly estimatethe SOC of a secondary battery that is being charged/discharged.Examples of such a conventional method for estimating an SOC include thefollowing two kinds of methods.

(1) A charging/discharging current is measured. The value of the current(having a minus sign in the case of charging, and having a plus sign inthe case of discharging) is multiplied by a charging efficiency. Themultiplied values are accumulated over a certain period of time tocalculate an accumulated capacity. Then, an SOC is estimated based onthe accumulated capacity.

(2) A plurality of data sets of charging/discharging currents andterminal voltages of a secondary battery corresponding thereto aremeasured and stored. A primary approximate line (voltage V—current Iapproximate line) is obtained from the data sets by least squares, and avoltage value (V intercept of a V-I approximate line) corresponding to acurrent value 0 (zero) is calculated as a no-load voltage (V0). Then, anSOC is estimated based on the no-load voltage V0.

Furthermore, when a secondary battery is charged/discharged, apolarization voltage is generated with respect to a batteryelectromotive force. More specifically, a voltage increases duringcharging, whereas a voltage decreases during discharging. This change iscalled a polarization voltage. In the case of estimating an SOC from avoltage as in the above-mentioned method (2), in the case of estimatingan increase and a decrease in a voltage during predetermined time, andin the case of obtaining electric power that can be input/output duringpredetermined time, it is necessary to grasp a polarization voltageexactly.

In general, as a method for estimating a polarization voltage, a primaryregression line is obtained from a plurality of current and voltagedata, the slope of the line is set to be a polarization resistance(component resistance, reaction resistance, and diffusion resistance),and the polarization resistance is multiplied by a current to obtain apolarization voltage.

However, the above-mentioned two kinds of conventional SOC estimationmethods have the following problems.

First, in the case of the SOC estimation method based on an accumulatedcapacity in the above method (1), a charging efficiency required foraccumulating current values depends upon an SOC value, a current value,a temperature, and the like. Therefore, it is difficult to find acharging efficiency suitable for these various kinds of conditions.Furthermore, in the case where a battery is being left, a self-dischargeamount during that time cannot be calculated. For these reasons and thelike, the difference between the true value of an SOC and the estimatedvalue thereof increases with the passage of time. Therefore, in order toeliminate this, it is necessary to perform complete discharging or fillcharging to initialize the SOC.

However, in the case where a secondary battery is mounted on an HEV,when complete discharging is performed, the secondary battery cannotsupply electric power, which becomes a burden on an engine. Therefore,it is necessary to charge a secondary battery over a predeterminedperiod of time until it is fully charged after stopping a vehicle at acharging site and the like and completely discharging the secondarybattery. Thus, in the case of the application to an HEV, it isimpossible to perform complete charging/discharging during driving of avehicle so as to initialize an SOC. Furthermore, to periodically performcomplete charging/discharging of a secondary battery mounted on an HEVis inconvenient for a user, and also becomes a burden on the user.

Next, in the case of the SOC estimation method based on a no-loadvoltage in the above method (2), first, a V intercept of a V-Iapproximate line after large discharging becomes relatively low, and a Vintercept of the V-I approximate line after large charging becomesrelatively high. Thus, a no-load voltage is varied even at the same SOC,depending upon the past history of a charging/discharging current. Thischange is caused by a polarization voltage. Accordingly, the no-loadvoltage that is a V intercept of a V-I approximate line is variedbetween a charging direction and a discharging direction, due to thefactor of a polarization voltage. Because of this, the difference involtage turns to be an estimation error of an SOC. Furthermore, adecrease in voltage due to a memory effect and leaving of a battery,battery degradation, and the like also cause an estimation error of anSOC.

Furthermore, according to the above-mentioned conventional method forestimating a polarization voltage, when a polarization voltage isobtained by a polarization resistance, a reaction resistance due to thereaction between an active material of a battery and an interface of anelectrolyte solution and a diffusion resistance due to the reaction inactive materials, between active materials, and in an electrolytesolution, included in a polarization resistance, cannot be estimatedsufficiently. Therefore, the accuracy of an estimated polarizationvoltage is unsatisfactory. Accordingly, it is not practical to use ano-load voltage in the above method (2) for correction, in order toobtain a battery electromotive force for estimating an SOC.

DISCLOSURE OF INVENTION

The present invention has been achieved in view of the above problems,and its object is to provide a method and apparatus for estimating anSOC with high accuracy, without periodically performing completecharging/discharging of a secondary battery to initialize the SOC; abattery pack system with a computer system (electronic control unit fora battery (battery ECU)) for performing processing in the method mountedthereon; and a motor-driven vehicle with the battery pack system mountedthereon.

In order to achieve the above-mentioned object, a first method forestimating a remaining capacity of a secondary battery according to thepresent invention includes the steps of: measuring data sets of acurrent flowing through a secondary battery and a terminal voltage ofthe secondary battery corresponding to the current, and obtaining aplurality of the data sets; calculating an electromotive force of thesecondary battery based on the obtained plurality of data sets;determining a correction amount with respect to a current accumulationcoefficient in accordance with the calculated electromotive force;calculating the current accumulation coefficient from the correctionamount and a charging efficiency; and multiplying the calculated currentaccumulation coefficient by the measured current, and estimating aremaining capacity of the secondary battery by current accumulation.

In order to achieve the above-mentioned object, a second method forestimating a remaining capacity of a secondary battery according to thepresent invention includes the steps of: measuring data sets of acurrent flowing through a battery pack including a combination of aplurality of cells that are secondary batteries and used in anintermediately charged state and a terminal voltage of the secondarybattery corresponding to the current, and obtaining a plurality of thedata sets; calculating an electromotive force of the secondary batterybased on the obtained plurality of data sets; determining a correctionamount with respect to a current accumulation coefficient in accordancewith the calculated electromotive force; calculating the currentaccumulation coefficient from the correction amount and a chargingefficiency; and multiplying the calculated current accumulationcoefficient by the measured current, and estimating a remaining capacityof the secondary battery by current accumulation.

According to the above-mentioned methods, the current accumulationcoefficient is corrected in accordance with a battery electromotiveforce and an SOC is estimated by current accumulation. Thus, an errordue to the current accumulation is not accumulated in an SOCintermediate region, and an SOC can be estimated with high accuracy.

Furthermore, the SOC after self-discharging caused by being left for along period of time, etc. also can be estimated easily, and it is notrequired to initialize an SOC by performing complete discharging andcomplete charging periodically.

It is preferable that the first and second methods for estimating aremaining capacity of a secondary battery further include the steps ofmeasuring a temperature of a secondary battery, and calculating acharging efficiency during charging based on the measured temperature,current, and estimated remaining capacity.

According to the above method, the temperature change, current change,and remaining capacity estimated value of a battery are fed back,whereby the calculation accuracy of an accumulated capacity can beenhanced.

In the first and second methods for estimating a remaining capacity of asecondary battery, it is preferable that the step of determining acorrection amount includes the steps of previously obtainingcharacteristics of an electromotive force with respect to a remainingcapacity, and calculating an estimated electromotive force from anestimated remaining capacity based on a look-up table or a formulastoring the characteristics; and determining a correction amount basedon a difference value between the electromotive force obtained in thestep of calculating an electromotive force and the estimatedelectromotive force.

According to the above method, the remaining capacity estimated value isfed back as an estimated electromotive force, and the difference valuebetween the calculated electromotive force and the estimatedelectromotive force is controlled to be zero, whereby the calculationaccuracy of an accumulated capacity can be enhanced further.

Furthermore, in the first and second methods for estimating a remainingcapacity of a secondary battery, it is preferable that the step ofcalculating an electromotive force includes the step of obtaining ano-load voltage that is a voltage intercept corresponding to a currentvalue 0 in an approximate line obtained by statistical processing usingleast squares with respect to a plurality of data sets, and calculatinga no-load voltage as an electromotive force.

According to the above method, the current accumulation coefficient canbe corrected in accordance with an electromotive force with a simpleconfiguration.

Alternatively, in the first and second methods for estimating aremaining capacity of a secondary battery, it is preferable that thestep of calculating an electromotive force includes the steps of:calculating a variation of an accumulated capacity during a pastpredetermined period from a measured current; calculating a polarizationvoltage based on the variation of the accumulated capacity; calculatinga no-load voltage that is a voltage intercept corresponding to a currentvalue 0 in an approximate line obtained by statistical processing usingleast squares with respect to a plurality of data sets; and subtractingthe polarization voltage from the no-load voltage to calculate anelectromotive force.

According to the above method, the polarization voltage is calculatedbased on the variation of an accumulated capacity. Therefore, thecalculation accuracy of a polarization voltage is satisfactory, and thecalculation accuracy of a battery electromotive force (equilibriumpotential) obtained by subtracting a polarization voltage from a no-loadvoltage is satisfactory. This makes it possible to estimate an SOC withhigh accuracy.

In the first and second methods for estimating a remaining capacity of asecondary battery, it is preferable that the step of calculating anelectromotive force includes the step of subjecting the variation of anaccumulated capacity to time delay processing.

According to the above method, the polarization voltage having a delaytime with respect to the variation of an accumulated capacity can becalculated so as to follow the variation of an accumulated capacity inreal time.

Furthermore, in the first and second methods for estimating a remainingcapacity of a secondary battery, it is preferable that averagingprocessing by filtering as well as time delay processing are performedwith respect to the variation of an accumulated capacity.

According to the above method, a fluctuation component of an accumulatedcapacity that is not necessary for calculating a polarization voltagecan be reduced.

Furthermore, in the first and second methods for estimating a remainingcapacity of a secondary battery, it is preferable that the step ofcalculating an electromotive force includes the step of subjecting apolarization voltage to time delay processing.

According to the above method, the timing between the no-load voltageand the polarization voltage can be adjusted, and an appropriateelectromotive force can be calculated.

In this case, it is preferable that averaging processing by filtering aswell as time delay processing are performed with respect to apolarization voltage.

According to the above method, a fluctuation component of a polarizationvoltage that is not necessary for calculating an electromotive force canbe reduced.

It is preferable that the first and second methods for estimating aremaining capacity of a secondary battery further include the step ofselecting a plurality of obtained data sets based on a predeterminedselection condition, wherein a plurality of data sets are selected inthe case where as a predetermined selection condition, a value of acurrent is in a predetermined range on a charging side and a dischargingside, there are a predetermined number or more of data sets on thecharging side and the discharging side, and a variation of anaccumulated capacity while a plurality of data sets are being obtainedis in a predetermined range.

According to the above method, a plurality of data sets can be obtaineduniformly on a charging side and a discharging side without beinginfluenced by a variation of an accumulated capacity.

It is preferable that the first and second methods for estimating aremaining capacity of a secondary battery further include the step ofdetermining whether or not a calculated no-load voltage is effectivebased on a predetermined determination condition, wherein a calculatedno-load voltage is determined to be effective in the case where as apredetermined determination condition, a variance of a plurality of datasets with respect to an approximate line obtained by statisticalprocessing using least squares is in a predetermined range, or acorrelation coefficient between the approximate line and the pluralityof data sets is a predetermined value or more.

According to the above method, the calculation accuracy of a no-loadvoltage can be enhanced.

In the first and second methods for estimating a remaining capacity of asecondary battery, a secondary battery is a nickel-metal hydridesecondary battery.

In order to achieve the above-mentioned object, a first battery packsystem according to the present invention includes a computer system forperforming the second method for estimating a remaining capacity of asecondary battery and a battery pack.

In order to achieve the above-mentioned object, a first motor-drivenvehicle according to the present invention has a first battery packsystem mounted thereon.

According to the above configuration, in the case where, as amicrocomputer system, for example, a battery pack system with a batteryECU mounted thereon is mounted on, for example, an HEV, etc., an SOC canbe controlled exactly based on the SOC estimated with high accuracy.More specifically, in the case where the SOC estimated by computation(SOC estimated value) is determined to be higher than a true SOC (SOCtrue value), the charging efficiency is reduced by a correction amountof the current accumulation coefficient. As a result, the SOC estimatedvalue is decreased at subsequent accumulation, compared with theprevious accumulation, so that the SOC estimated value is approximatedto the SOC true value. On the other hand, in the case where the SOCestimated value is determined to be lower than the SOC true value, thecharging efficiency is added by a correction amount of the currentaccumulation coefficient. As a result, the SOC estimated value isincreased at subsequent accumulation, compared with the previousaccumulation, so that the SOC estimated value also is approximated tothe SOC true value. Thus, by continuing this control, the SOC estimatedvalue and the SOC true value are managed so as to be always matched witheach other, and the deviation of the SOC estimated value with respect tothe SOC true value is decreased. This can remarkably enhance theaccuracy of energy management of an entire system.

In order to achieve the above-mentioned object, a first apparatus forestimating a remaining capacity of a secondary battery according to thepresent invention includes: a current measuring section for measuring acurrent flowing through a secondary battery as current data; a voltagemeasuring section for measuring a terminal voltage of the secondarybattery corresponding to the current as voltage data; an electromotiveforce calculation section for calculating an electromotive force of thesecondary battery based on a plurality of data sets of the current datafrom the current measuring section and the voltage data from the voltagemeasuring section; a current accumulation coefficient correction sectionfor determining a correction amount with respect to a currentaccumulation coefficient in accordance with the electromotive force fromthe electromotive force calculation section; an adder for outputting thecurrent accumulation coefficient from the correction amount from thecurrent accumulation coefficient correction section and a chargingefficiency; and a remaining capacity estimation section for multiplyingthe current accumulation coefficient from the adder by the current data,and estimating a remaining capacity of the secondary battery by currentaccumulation.

In order to achieve the above-mentioned object, a second apparatus forestimating a remaining capacity of a secondary battery according to thepresent invention includes: a current measuring section for measuring acurrent flowing through a battery pack having a combination of aplurality of cells that are secondary batteries and used in anintermediately charged state, as current data; a voltage measuringsection for measuring a terminal voltage of the secondary batterycorresponding to the current as voltage data; an electromotive forcecalculation section for calculating an electromotive force of thesecondary battery, based on the plurality of data sets of the currentdata from the current measuring section and the voltage data from thevoltage measuring section; a current accumulation coefficient correctionsection for determining a correction amount with respect to a currentaccumulation coefficient, in accordance with the electromotive forcefrom the electromotive force calculation section; an adder foroutputting the current accumulation coefficient from the correctionamount from the current accumulation coefficient correction section anda charging efficiency; and a remaining capacity estimation section formultiplying the current accumulation coefficient from the adder by thecurrent data, and estimating the remaining capacity of a secondarybattery by current accumulation.

According to the above configuration, the current accumulationcoefficient is corrected in accordance with a battery electromotiveforce and an SOC is estimated by current accumulation. Thus, an errordue to the current accumulation is not accumulated in an SOCintermediate region, and an SOC can be estimated with high accuracy.

Furthermore, the SOC after self-discharging caused by being left for along period of time, etc. also can be estimated easily, and it is notrequired to initialize an SOC by performing complete discharging andcomplete charging periodically.

It is preferable that the first and second apparatuses for estimating aremaining capacity of a secondary battery further includes a temperaturemeasuring section for measuring a temperature of a secondary battery astemperature data, and a charging efficiency calculation section forcalculating a charging efficiency during charging based on thetemperature from the temperature measuring section, the current from thecurrent measuring section, and the remaining capacity estimated valuefrom the remaining capacity estimation section.

According to the above configuration, the temperature change andremaining capacity estimated value of a battery are fed back to acharging efficiency, whereby the calculation accuracy of an accumulatedcapacity can be enhanced.

Furthermore, it is preferable that the first and second apparatuses forestimating a remaining capacity of a secondary battery further includesan estimated electromotive force calculation section for calculating anestimated electromotive force from a remaining capacity estimated valuebased on a previously obtained look-up table or a formula storing thecharacteristics of an electromotive force with respect to a remainingcapacity, and the current accumulation coefficient correction sectiondetermines a correction amount based on a difference value between theelectromotive force from the electromotive force calculation section andthe estimated electromotive force.

According to the above configuration, the remaining capacity estimatedvalue is fed back as an estimated electromotive force, and thedifference value between the calculated electromotive force and theestimated electromotive force is controlled to be zero, whereby thecalculation accuracy of an accumulated capacity can be enhanced further.

In the first and second apparatuses for estimating a remaining capacityof a secondary battery, it is preferable that the electromotive forcecalculation section obtains a no-load voltage that is a voltageintercept corresponding to a current value 0 in an approximate lineobtained by statistical processing using least squares with respect to aplurality of data sets, and calculating a no-load voltage as anelectromotive force.

According to the above configuration, the current accumulationcoefficient can be corrected in accordance with an electromotive forcewith a simple configuration.

In the first and second apparatuses for estimating a remaining capacityof a secondary battery, it is preferable that the electromotive forcecalculation section includes: a varied capacity calculation section forcalculating a variation of an accumulated capacity during a pastpredetermined period from current data; a polarization voltagecalculation section for calculating a polarization voltage based on thevariation of the accumulated capacity from the varied capacitycalculation section; a no-load voltage calculation section forcalculating a no-load voltage that is a voltage intercept correspondingto a current value 0 in an approximate line obtained by statisticalprocessing using least squares with respect to a plurality of data sets;and a subtractor for subtracting the polarization voltage from theno-load voltage to output an electromotive force.

According to the above configuration, the polarization voltage iscalculated based on the variation of an accumulated capacity. Therefore,the calculation accuracy of a polarization voltage is satisfactory, andthe calculation accuracy of a battery electromotive force (equilibriumpotential) obtained by subtracting a polarization voltage from a no-loadvoltage is satisfactory. This makes it possible to estimate an SOC withhigh accuracy.

It is preferable that the first or second apparatuses for estimating aremaining capacity of a secondary battery further includes a firstcomputation section for subjecting the variation of an accumulatedcapacity from the varied capacity calculation section to time delayprocessing.

According to the above configuration, the polarization voltage having adelay time with respect to the variation of an accumulated capacity canbe calculated so as to follow the variation of an accumulated capacityin real time.

Furthermore, in the first or second apparatuses for estimating aremaining capacity of a secondary battery, it is preferable that thefirst computation section subjects the variation of an accumulatedcapacity to averaging processing by filtering, as well as time delayprocessing

According to the above configuration, a fluctuation component of anaccumulated capacity that is not necessary for calculating apolarization voltage can be reduced.

It is preferable that the first or second apparatus for estimating aremaining capacity of a secondary battery includes a second computationsection for subjecting a polarization voltage to time delay processing.

According to the above configuration, the timing between the no-loadvoltage and the polarization voltage can be adjusted, and an appropriateelectromotive force can be calculated.

In this case, it is preferable that the second computation sectionperforms averaging processing by filtering, as well as time delayprocessing.

According to the above configuration, a fluctuation component of apolarization voltage that is not necessary for calculating anelectromotive force can be reduced.

Furthermore, it is preferable that the first or second apparatus forestimating a remaining capacity of a secondary battery further includesa data set selection section for selecting a plurality of data setsbased on a predetermined selection condition and outputting them to theno-load voltage calculation section, wherein the data set selectionsection selects a plurality of data sets in the case where as apredetermined selection condition, a value of a current is in apredetermined range on a charging side and a discharging side, there area predetermined number or more of data sets on the charging side and thedischarging side, and a variation of an accumulated capacity while aplurality of data sets are being obtained is in a predetermined range.

According to the above configuration, a plurality of data sets can beobtained uniformly on a charging side and a discharging side withoutbeing influenced by a variation of an accumulated capacity.

Furthermore, it is preferable that the first or second apparatus forestimating a remaining capacity of a secondary battery further includesa no-load voltage determination section for determining whether or not ano-load voltage calculated in the no-load voltage calculation section iseffective based on a predetermined determination condition, wherein theno-load voltage determination section determines the calculated no-loadvoltage to be effective in the case where as a predetermineddetermination condition, a variance of a plurality of data sets withrespect to an approximate line obtained by statistical processing usingleast squares is in a predetermined range, or a correlation coefficientbetween the approximate line and the plurality of data sets is apredetermined value or more.

According to the above configuration, the calculation accuracy of ano-load voltage can be enhanced.

In the first and second apparatuses for estimating a remaining capacityof a secondary battery, a secondary battery is a nickel-metal hydridesecondary battery.

In order to achieve the above-mentioned object, the second battery packsystem according to the present invention includes the second apparatusfor estimating a remaining capacity of a secondary battery, and abattery pack. In this case, it is preferable that the second apparatusfor estimating a remaining capacity of a secondary battery is configuredas a computer system.

In order to achieve the above-mentioned object, a second motor-drivenvehicle according to the present invention has the second battery packsystem mounted thereon.

According to the above configuration, in the case where, as amicrocomputer system, for example, a battery pack system with a batteryECU mounted thereon is mounted on, for example, an HEV, etc., an SOC canbe controlled exactly based on the SOC estimated with high accuracy.More specifically, in the case where the SOC estimated by computation(SOC estimated value) is determined to be higher than a true SOC (SOCtrue value), the charging efficiency is reduced by a correction amountof the current accumulation coefficient. As a result, the SOC estimatedvalue is decreased at subsequent accumulation, compared with theprevious accumulation, so that the SOC estimated value is approximatedto the SOC true value. On the other hand, in the case where the SOCestimated value is determined to be lower than the SOC true value, thecharging efficiency is added by a correction amount of the currentaccumulation coefficient. As a result, the SOC estimated value isincreased at subsequent accumulation, compared with the previousaccumulation, so that the SOC estimated value also is approximated tothe SOC true value. Thus, by continuing this control, the SOC estimatedvalue and the SOC true value are managed so as to be always matched witheach other, and the deviation of the SOC estimated value with respect tothe SOC true value is decreased. This can remarkably enhance theaccuracy of energy management of an entire system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an exemplary configuration of abattery pack system according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing data sets of voltage data V(n) and currentdata I(n) and an approximate line for obtaining a no-load voltage V0from the data sets by statistical processing.

FIG. 3 is a flow chart showing a processing procedure in a method forestimating a remaining capacity of a secondary battery according toEmbodiment 1 of the present invention.

FIG. 4 is a block diagram showing an exemplary configuration of abattery pack system according to Embodiment 2 of the present invention.

FIG. 5 is a flow chart showing a processing procedure in a method forestimating a remaining capacity of a secondary battery according toEmbodiment 2 of the present invention.

FIG. 6 is a block diagram showing an exemplary configuration of abattery pack system according to Embodiment 3 of the present invention.

FIG. 7 is a diagram showing an example of a variation ΔQ of anaccumulated capacity and a change in a polarization voltage Vpol withthe passage of time in Embodiment 3.

FIG. 8 is a flow chart showing a processing procedure in a method forestimating a remaining capacity of a secondary battery according toEmbodiment 3 of the present invention.

FIG. 9 is a diagram showing a change with the passage of time in ano-load voltage V0, an electromotive force Veq, a current accumulationcoefficient k, an SOC true value (SOCt), and an SOC estimated value(SOCes) in Embodiment 3.

FIG. 10 shows the convergence of an SOC estimated value in the casewhere the initial value at a time of estimation of an SOC is changed inEmbodiment 3.

FIG. 11 is a block diagram showing an exemplary configuration of abattery pack system according to Embodiment 4 of the present invention.

FIG. 12 is a flow chart showing a processing procedure in a method forestimating a remaining capacity of a secondary battery according toEmbodiment 4 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described by way of preferredembodiments with reference to the drawings.

Embodiment 1

FIG. 1 is a block diagram showing an exemplary configuration of abattery pack system 1A according to Embodiment 1 of the presentinvention. In FIG. 1, the battery pack system 1A is composed of abattery pack 100 and a battery ECU 101A including an apparatus forestimating a remaining capacity according to the present invention as apart of a microcomputer system.

The battery pack 100 has a configuration in which a plurality of batterymodules (cells), each having a plurality of cells (e.g., nickel-metalhydride batteries) electrically connected in series, are electricallyconnected in series, so as to obtain a predetermined output, generallywhen mounted on an HEV, etc.

In the battery ECU 101A, reference numeral 102 denotes a voltagemeasuring section for measuring a terminal voltage of the secondarybattery 100 detected by a voltage sensor (not shown) at a predeterminedsampling period as voltage data V(n), 103 denotes a current measuringsection for measuring a charging/discharging current of the secondarybattery 100 detected by a current sensor (not shown) at a predeterminedsampling period as current data I(n) (the sign of which represents acharging direction or a discharging direction), and 104 denotes atemperature measuring section for measuring a temperature of thesecondary battery 100 detected by a temperature sensor (not shown) astemperature data T(n).

Reference numeral 105 denotes an electromotive force calculationsection, which is composed of a data set selection section 106, ano-load voltage calculation section 107, and a no-load voltagedetermination section 108.

The voltage data V(n) from the voltage measuring section 102 and thecurrent data I(n) from the current measuring section 103 are input tothe data set selection section 106 as data sets. In the data setselection section 106, in the case where as a selection condition, thevalues of the current data I(n) in a charging direction (−) and adischarging direction (+) are in a predetermined range (e.g., ±50 A),there are a predetermined number or more (e.g., each 10 among 60samples) of current data I(n) in the charging direction and thedischarging direction, and the variation ΔQ of the accumulated capacitywhile data sets are being obtained is in a predetermined range (e.g.,0.3 Ah), the data sets of the voltage data V(n) and the current dataI(n) are determined to be effective, and they are selected and output aseffective data sets S(V(n), I(n)).

The effective data sets S(V(n), I(n)) from the data set selectionsection 106 are input to the no-load voltage calculation section 107. Inthe no-load voltage calculation section 107, as shown in FIG. 2, aprimary voltage-current line (approximate line) is obtained from theeffective data sets S(V(n), I(n)) by statistical processing using leastsquares, and a voltage value (voltage (V) intercept) corresponding to 0current is calculated as a no-load voltage V0.

The no-load voltage V0 from the no-load voltage calculation section 107is input to the no-load voltage determination section 108. In theno-load voltage determination section 108, in the case where as adetermination condition, a variance of the data sets S(V(n), I(n)) withrespect to the approximate line is obtained and this variance is in apredetermined range, or a correlation coefficient between theapproximate line and the data sets S(V(n), I(n)) is obtained and thiscorrelation coefficient is a predetermined value or greater, thecalculated no-load voltage V0 is determined to be effective and isoutput as an electromotive force Veq of a battery.

The electromotive force Veq from the electromotive force calculationsection 105 is input to a current accumulation coefficient correctionsection 109. In the current accumulation coefficient correction section109, a correction amount α with respect to a current accumulationcoefficient k is determined in accordance with the electromotive forceVeq. The correction amount α with respect to the electromotive force Veqis represented by a primary expression, which is determined consideringthe convergence of a system. The correction amount α obtained in thecurrent accumulation coefficient correction section 109 is added to orsubtracted from a charging efficiency η output from a chargingefficiency calculation section 110 by an adder 111 to obtain the currentaccumulation coefficient k The current accumulation coefficient k fromthe adder 111 is input to a remaining capacity estimation section 112.In the remaining capacity estimation section, the current data I(n) fromthe current measuring section 103 is multiplied by the currentaccumulation coefficient k, and a remaining capacity SOC is estimated bycurrent accumulation during a predetermined period of time.

Furthermore, the SOC estimated value is input to the charging efficiencycalculation section 110. In the charging efficiency calculation section110, the charging efficiency η is calculated from previously storedcharacteristic curves of the charging efficiency η with respect to theSOC estimated value with a temperature being a parameter, based ontemperature data T(n), which is measured in the temperature measuringsection 104. In the case where the battery pack 100 is in a dischargedstate, the charging efficiency η is fixed to 1. In the case where thebattery pack 100 is in a charged state, the charging efficiency ηcalculated by the charging efficiency calculation section 110 is used.

Next, the processing procedure of estimating a remaining capacity in abattery pack system as configured above will be described with referenceto FIG. 3.

FIG. 3 is a flow chart showing the processing procedure in the methodfor estimating a remaining capacity of a secondary battery according toEmbodiment 1 of the present invention. In FIG. 3, voltage data V(n) andcurrent data I(n) are measured as data sets (S301). Then, in order toexamine whether or not the data sets of the voltage data V(n) and thecurrent data I(n) measured in Step S301 are effective, it is determinedwhether or not these data sets satisfy the selection condition asdescribed above (S302). In the case where the data sets do not satisfythe selection condition in the determination in Step S302 (No), theprocess returns to Step S301, and the data sets of the voltage data V(n)and the current data I(n) are measured again. On the other hand, in thecase where the data sets satisfy the selection condition in thedetermination in Step S302 (Yes), the process proceeds to Step S303, anda plurality of (e.g., each 10 in the charging and discharging directionsamong 60 samples) effective data sets S(V(n), I(n)) are obtained (S303).

Next, a primary approximate line (V-I line) is obtained from theeffective data sets S(V(n), I(n)), by statistical processing using leastsquares. A V intercept of the approximate line is calculated as ano-load voltage V0 (S304). Then, in order to examine whether or not theno-load voltage V0 calculated in Step S304 is effective, it isdetermined whether or not the no-load voltage V0 satisfies theabove-mentioned determination condition (S305). In the case where theno-load voltage V0 does not satisfy the determination condition in thedetermination in Step S305 (No), the process returns to Step S303. Then,another plurality of (e.g., different each 10 among 60 samples)effective data sets S(V(n), I(n)) are obtained, and Steps S304 and S305are repeated. On the other hand, in the case where the calculatedno-load voltage V0 satisfies the determination condition in thedetermination in Step S305 (Yes), the calculated no-load voltage V0 isset to be an electromotive force Veq.

Then, a correction amount α with respect to a current accumulationcoefficient k is calculated in accordance with the electromotive forceVeq (S306). Furthermore, a charging efficiency η is calculated from aremaining capacity SOC (SOC estimated value) that is currentlyestimated, based on measured temperature data T(n) (S307). Then, thecorrection amount α obtained in Step S306 is added to the chargingefficiency η obtained in Step S307 to calculate the current accumulationefficient k (S308). Finally, the current data I(n) is multiplied by thecurrent accumulation coefficient k, and a remaining capacity SOC isestimated by current accumulation during a predetermined period (S309).

As described above, according to the present embodiment, the currentaccumulation coefficient k is corrected in accordance with the batteryelectromotive force Veq, and an SOC is estimated by currentaccumulation, whereby an error due to current accumulation is notaccumulated in an SOC intermediate region, and an SOC can be estimatedwith high accuracy.

Embodiment 2

FIG. 4 is a block diagram showing an exemplary configuration of abattery pack system according to Embodiment 2 of the present invention.In FIG. 4, the same components as those shown in FIG. 1 representing theconfiguration of Embodiment 1 are denoted with the same referencenumerals as those therein, and the description thereof will be omittedhere.

In the present embodiment, an estimated electromotive force calculationsection 113 and a subtractor 114 are added to Embodiment 1 to configurea battery ECU 101B.

The estimated electromotive force calculation section 113 obtains anestimated electromotive force Ves from a currently estimated SOC. Thesubtractor 114 subtracts the estimated electromotive force Ves, which iscalculated in the estimated electromotive force calculation section 113,from the electromotive force Veq, which is calculated in theelectromotive force calculation section 105, and outputs anelectromotive force deviation Vd to the current accumulation coefficientcorrection section 109.

Next, the processing procedure of estimating a remaining capacity in abattery pack system as configured above will be described with referenceto FIG. 5.

FIG. 5 is a flow chart showing the processing procedure in the methodfor estimating a remaining capacity of a secondary battery according toEmbodiment 2 of the present invention. In FIG. 5, the same processingsteps as those in FIG. 3 representing the processing procedure ofEmbodiment 1 are denoted with the same reference numerals, and thedescription thereof will be omitted here.

In FIG. 5, the steps up to the determination step of a no-load voltageV0 (S305) are the same as those in Embodiment 1, so that the descriptionthereof will be omitted here. In the case where the calculated no-loadvoltage V0 satisfies the determination condition in the determination inStep S305 (Yes), an estimated electromotive force Ves is calculated fromthe SOC estimated value, based on a previously obtained look-up table orformula storing characteristics of an electromotive force with respectto a remaining capacity (S501). Then, the estimated electromotive forceVes is subtracted from the electromotive force Veq determined in StepS305 to calculate an electromotive force deviation Vd (S502). Then, thecorrection amount α with respect to the current accumulation coefficientk is calculated in accordance with the electromotive force deviation Vd(S503).

The subsequent steps are the same as those in Embodiment 1, so that thedescription thereof will be omitted here.

As described above, according to the present embodiment, an SOCestimated value is fed back as the estimated electromotive force Ves,and a difference value between the calculated electromotive force Veqand the estimated electromotive force Ves is controlled to be zero,whereby the calculation accuracy of the accumulated capacity can befurther enhanced.

Embodiment 3

FIG. 6 is a block diagram showing an exemplary configuration of abattery pack system 1C according to Embodiment 3 of the presentinvention. In FIG. 6, the same components as those shown in FIG. 4representing the configuration of Embodiment 2 are denoted with the samereference numerals as those therein, and the description thereof will beomitted here.

In the present embodiment, a varied capacity calculation section 115, afirst computation section 116, a polarization voltage calculationsection 117, and a subtractor 118 are added to the electromotive forcecalculation section 105 of Embodiment 2 to obtain an electromotive forcecalculation section 105′, whereby a battery ECU 101C is configured.

The varied capacity calculation section 115 obtains a variation ΔQ ofthe accumulated capacity during a past predetermined period (e.g., oneminute) from the current data I(n).

The first computation section 116 functions as a low-pass filter (LPF).The first computation section 116 performs time delay processing foradjusting the timing between the variation ΔQ of the accumulatedcapacity from the varied capacity calculation section 115 and apolarization voltage Vpol obtained in the subsequent polarizationvoltage calculation section 117, and averaging processing for removing afluctuation component corresponding to an unnecessary high-frequencycomponent in the variation ΔQ of the accumulated capacity, and outputsthe results as LPF (ΔQ). Herein, FIG. 7 shows, as an example, thevariation ΔQ of the accumulated capacity during the past one minute as asolid line, and the polarization voltage Vpol as a broken line. It isunderstood from FIG. 7 that the polarization voltage Vpol is changedafter tens of seconds from the variation ΔQ of the accumulated capacityduring the past one minute. Corresponding to this time delay, a timeconstant τ of the LPF (in the present embodiment, the LPF is composed ofa primary delay element) constituting the first computation section 116is determined. The time constant τ is determined so that a primary delayelement is computed with respect to ΔQ, and a correlation coefficientbetween the LPF (ΔQ) and the polarization voltage Vpol is maximized.

In the polarization voltage calculation section 117, the polarizationvoltage Vpol is calculated based on the temperature data T(n) measuredin the temperature measuring section 104, from a characteristic curve ora formula of the polarization voltage Vpol with respect to the LPF (ΔQ)with a temperature being a parameter, previously stored in a look-uptable (LUT) 1171.

The subtractor 118 substrates the polarization voltage Vpol from theeffective electromotive force V0_(OK) to output an electromotive forceVeq.

Next, the processing procedure of estimating a remaining capacity in abattery pack system as configured above will be described with referenceto FIG. 8.

FIG. 8 is a flow chart showing the processing procedure in the methodfor estimating a remaining capacity of a secondary battery according toEmbodiment 3 of the present invention. In FIG. 8, the same processingsteps as those in FIG. 5 representing the processing procedure ofEmbodiment 2 are denoted with the same reference numerals as thosetherein, and the description thereof will be omitted here.

In FIG. 8, the steps up to the determination step of a no-load voltageV0 (S305) are the same as those in Embodiment 1, so that the descriptionthereof will be omitted here. In the present embodiment, a variation ΔQof an accumulated capacity during a past predetermined period (e.g., oneminute) is obtained from the current data I(n) measured in Step S301(S1001). Then, the variation ΔQ of the accumulated capacity is subjectedto filtering (time delay and averaging processing) to compute LPF (ΔQ)(S1002). Then, a polarization voltage Vpol is calculated from thecomputed LPF (ΔQ), based on a look-up table or formula which storesprevious polarization voltage Vpol-LPF (ΔQ) characteristic data with thetemperature data T(n) being a parameter (S1003).

Next, the polarization voltage Vpol calculated in Step S1003 issubtracted from the effective no-load voltage V0_(OK) determined in StepS305 to calculate an electromotive force Veq (S1004).

The subsequent steps are the same as those in Embodiment 2, so that thedescription thereof will be omitted here.

FIG. 9 is a diagram showing a change with the passage of time in ano-load voltage V0, an electromotive force Veq, a current accumulationcoefficient k, an SOC true value (SOCt), and an SOC estimated value(SOCes). In FIG. 9, the polarization voltage Vpol is subtracted from theno-load voltage V0 to obtain an electromotive force Veq, and an SOC isestimated using the current accumulation coefficient k corrected inaccordance with the electromotive force Veq, whereby it is understoodthat the SOC estimated value SOCes follows the SOC true value SOCt.

FIG. 10 shows the convergence of an SOC estimated value in the casewhere an initial value at a time of estimation of an SOC is changed.FIG. 10 shows plotted data representing a change in an SOC estimatedvalue with the passage of time: P0 in the case where an initial value is3.9 Ah (SOC true value); P1 in the case where an initial value is 6.5Ah, P2 in the case where an initial value is 5.2 Ah; P3 in the casewhere an initial value is 2.6 Ah; and P4 in the case where an initialvalue is 1.3 Ah. As is understood from FIG. 10, even if the initialvalue is ±2.6 Ah (error of about ±67%) with respect to the true value(3.9 Ah), the SOC estimated value is converged to ±0.2 Ah (error ofabout ±15%) with respect to the true value (1.3 Ah) after about one hour(3600 seconds).

As described above, according to the present embodiment, thepolarization voltage Vpol is calculated based on the variation ΔQ of theaccumulated capacity. Therefore, the calculation accuracy of thepolarization voltage Vpol is satisfactory, and the calculation accuracyof the battery electromotive force Veq obtained by subtracting thepolarization voltage Vpol from the no-load voltage V0 is satisfactory,whereby an SOC can be estimated with high accuracy.

Furthermore, the variation ΔQ of the accumulated capacity is subjectedto filtering (time delay and averaging processing). Thus, thepolarization voltage Vpol having a time delay with respect to thevariation ΔQ of the accumulated capacity can be calculated so as tofollow the variation ΔQ of the accumulated capacity in real time.Furthermore, a fluctuation component of the accumulated capacity that isnot necessary for calculating the polarization voltage Vpol can bereduced.

Embodiment 4

FIG. 11 is a block diagram showing an exemplary configuration of abattery back system 1D according to Embodiment 4 of the presentinvention. In FIG. 11, the same components as those in FIG. 6representing the configuration of Embodiment 3 are denoted with the samereference numerals as those therein, and the description thereof will beomitted here.

In the present embodiment, the first computation section 115 is omittedfrom the electromotive force calculation section 105′ of Embodiment 3,and a second computation section 119 is provided instead to obtain anelectromotive force calculation section 105″, whereby a battery ECU 101Dis configured.

The second computation section 119 functions as a low-pass filter (LPF).The second computation section 119 performs time delay processing foradjusting the timing between the polarization voltage Vpol from thepolarization voltage calculation section 117 and the effective no-loadvoltage V0_(OK) from the no-load voltage determination section 108, andaveraging processing for removing a fluctuation component correspondingto an unnecessary high-frequency component in the polarization voltageVpol, and outputs the results as LPF (Vpol).

Next, the processing procedure of estimating a remaining capacity in abattery pack system as configured above will be described with referenceto FIG. 12.

FIG. 12 is a flow chart showing the processing procedure in the methodfor estimating a remaining capacity of a secondary battery according toEmbodiment 4 of the present invention. In FIG. 12, the same processingsteps as those in FIG. 8 representing the processing procedure ofEmbodiment 3 are denoted with the same reference numerals as thosetherein, and the description thereof will be omitted here.

In FIG. 12, the steps up to the determination step of a no-load voltageV0 (S305) and up to the variation calculation step (S1001) of theaccumulated capacity are the same as those in Embodiment 3, so that thedescription thereof will be omitted here.

A polarization voltage Vpol is calculated from the variation ΔQ of theaccumulated capacity obtained in Step S1001, based on a look-up table orformula, which stores previous polarization voltage Vpol-ΔQcharacteristic data with the temperature data T(n) being a parameter(S1201). Then, the calculated polarization voltage Vpol is subjected tofiltering (time delay and averaging processing) to compute LPF (Vpol)(S1202). Then, the polarization voltage LPF (Vpol) after filtering,which was computed in Step S1202, is subtracted from the effectiveno-load voltage V0_(OK) which was determined in Step S305, to calculatean electromotive force Veq.

The subsequent steps are the same as those in Embodiment 3, so that thedescription thereof will be omitted here.

As described above, according to the present embodiment, thepolarization voltage Vpol is subjected to filtering (time delay andaveraging processing), whereby timing adjustment is performed betweenthe no-load voltage V0 and the polarization voltage Vpol, and anappropriate electromotive force Veq can be calculated. Furthermore, afluctuation component of the polarization voltage Vpol that is notrequired for calculating the electromotive force Veq can be reduced.

In the above-mentioned Embodiments 2 to 4, a predetermined period forcalculating the variation ΔQ of the accumulated capacity is set to be,for example, one minute. However, in the case where the battery packsystem is mounted on an HEV, etc., the predetermined period may bevaried depending upon a running state of a vehicle. More specifically,in the case where a secondary battery is charged/discharged frequently,the above-mentioned predetermined period is set to be short. In the casewhere a secondary battery is not charged/discharged frequently, theabove-mentioned predetermined period is set to be long. Thus, an optimumpolarization voltage can be estimated in accordance with an actualrunning state.

As described above, according to the present invention, the currentaccumulation coefficient is corrected in accordance with a batteryelectromotive force, and an SOC is estimated by current accumulation.Thus, an error due to current accumulation is not accumulated in an SOCintermediate region, and an SOC can be estimated with high accuracy.

Furthermore, the SOC after self-discharging caused by being left for along period of time, etc. also can be estimated easily, and it is notrequired to initialize an SOC by performing complete discharging andcomplete charging periodically.

Furthermore, in the case where the battery pack system is mounted on,for example, an HEV, etc., an SOC can be controlled exactly based on theSOC estimated with high accuracy. More specifically, in the case wherethe SOC estimated value is determined to be higher than an SOC truevalue, the charging efficiency is reduced by a correction amount of thecurrent accumulation coefficient. As a result, the SOC estimated valuealso is decreased at subsequent accumulation, compared with the previousaccumulation, so that the SOC estimated value is approximated to the SOCtrue value. On the other hand, in the case where the SOC estimated valueis determined to be lower than the SOC true value, the chargingefficiency is added by a correction amount of the current accumulationcoefficient. As a result, the SOC estimated value is increased atsubsequent accumulation, compared with the previous accumulation, sothat the SOC estimated value also is approximated to the SOC true value.Thus, by continuing this control, the SOC estimated value and the SOCtrue value are managed so as to be always matched with each other, andthe deviation of the SOC estimated value with respect to the SOC truevalue is decreased. This can remarkably enhance the accuracy of energymanagement of an entire system.

1. A method for estimating a remaining capacity of a secondary battery,comprising the steps of: measuring data sets of a current flowingthrough a secondary battery and a terminal voltage of the secondarybattery corresponding to the current, and obtaining a plurality of thedata sets; calculating an electromotive force of the secondary batterybased on the obtained plurality of data sets; determining a correctionamount with respect to a current accumulation coefficient in accordancewith the calculated electromotive force; calculating the currentaccumulation coefficient from the correction amount and a chargingefficiency; multiplying the calculated current accumulation coefficientby the measured current, and estimating a remaining capacity of thesecondary battery by current accumulation; and controlling the remainingcapacity by charging or discharging the secondary battery using theestimated remaining capacity of the secondary battery.
 2. A method forestimating a remaining capacity of a secondary battery, comprising thesteps of: measuring data sets of a current flowing through a batterypack including a combination of a plurality of cells that are secondarybatteries and used in an intermediately charged state and a terminalvoltage of the secondary battery corresponding to the current, andobtaining a plurality of the data sets; calculating an electromotiveforce of the secondary battery based on the obtained plurality of datasets; determining a correction amount with respect to a currentaccumulation coefficient in accordance with the calculated electromotiveforce; calculating the current accumulation coefficient from thecorrection amount and a charging efficiency; multiplying the calculatedcurrent accumulation coefficient by the measured current, and estimatinga remaining capacity of the secondary battery by current accumulation;and controlling the remaining capacity by charging of or discharging thesecondary battery using the estimated remaining capacity of thesecondary battery.
 3. A battery pack system comprising a computer systemfor executing the method for estimating a remaining capacity of asecondary battery of claim 2, and the battery pack.
 4. A motor-drivenvehicle on which a battery pack system comprising a computer system forperforming the method for estimating a remaining capacity of a secondarybattery of claim 2, and the battery pack.
 5. An apparatus for estimatinga remaining capacity of a secondary battery, comprising: a currentmeasuring section for measuring a current flowing through a secondarybattery as current data; a voltage measuring section for measuring aterminal voltage of the secondary battery corresponding to the currentas voltage data; an electromotive force calculation section forcalculating an electromotive force of the secondary battery based on aplurality of data sets of the current data from the current measuringsection and the voltage data from the voltage measuring section; acurrent accumulation coefficient correction section for determining acorrection amount with respect to a current accumulation coefficient inaccordance with the electromotive force from the electromotive forcecalculation section; an adder for outputting the current accumulationcoefficient from the correction amount from the current accumulationcoefficient correction section and a charging efficiency; and aremaining capacity estimation section for multiplying the currentaccumulation coefficient from the adder by the current data, andestimating a remaining capacity of the secondary battery by currentaccumulation.
 6. An apparatus for estimating a remaining capacity of asecondary battery, comprising: a current measuring section for measuringa current flowing through a battery pack having a combination of aplurality of cells that are secondary batteries and used in anintermediately charged state, as current data; a voltage measuringsection for measuring a terminal voltage of the secondary batterycorresponding to the current as voltage data; an electromotive forcecalculation section for calculating an electromotive force of thesecondary battery based on a plurality of data sets of the current datafrom the current measuring section and the voltage data from the voltagemeasuring section; a current accumulation coefficient correction sectionfor determining a correction amount with respect to a currentaccumulation coefficient, in accordance with the electromotive forcefrom the electromotive force calculation section; an adder foroutputting the current accumulation coefficient from the correctionamount from the current accumulation coefficient correction section anda charging efficiency; and a remaining capacity estimation section formultiplying the current accumulation coefficient from the adder by thecurrent data, and estimating the remaining capacity of a secondarybattery by current accumulation.
 7. A battery pack system comprising theapparatus for estimating a remaining capacity of a secondary battery ofclaim 6, and the battery pack.
 8. A motor-driven vehicle on which abattery pack system comprising the apparatus for estimating a remainingcapacity of a secondary battery of claim 6 and the battery pack ismounted.